A Satellite Study of Cloud Clusters over the Tropical North Atlantic Ocean

View More View Less
  • 1 Space Science and Engineering Center, The University of Wisconsin, Madison 53706
© Get Permissions
Restricted access

Signal enhancement is advanced as a method for isolating selected features of ATS images. The discussion covers enhancement theory, limitations, and one important application, the isolation of deep convection within tropical cloud clusters. Comparisons of brightness contoured ATS images with radar images from BOMEX test the validity of associating deep convection with very bright clouds. The enhancement technique is then applied in a census of Atlantic cloud clusters, and in case studies of individual clusters.

It is shown that in spite of difficulties involving control of the ATS signal, enhancement is an effective, precise tool for isolating selected features of ATS images. Comparisons of ATS and radar images establish a high correlation of bright areas on ATS with large radar echoes; therefore, enhanced ATS pictures emphasizing the upper levels of the brightness range effectively isolate deep convection. The brightness structure of convective clouds is such that they can be studied over a three-to four-hour period around local noon on pictures uncorrected for changes of incident and reflected radiation. A simple cosine law correction for incident radiation can appreciably extend this period.

The census and case studies show that the eastern Atlantic was at least as convectively active as the western Atlantic during June and July, 1969, and had a significantly greater total area of cloud clusters in 1969 and 1970. Convective cores have a great range of size, spacing, and lifetime: nevertheless, an ordering invariably can be perceived. This most often is in the form of lines or bands; waves, spirals, or solitary cores are also observed. Lifetimes are a few minutes to several hours or more; large cores last longer. Displacement of cloud clusters is accomplished by a complex combination of band and cell movement and propagation. Structure, as evidenced by core behavior, is varied and complex.

Signal enhancement is advanced as a method for isolating selected features of ATS images. The discussion covers enhancement theory, limitations, and one important application, the isolation of deep convection within tropical cloud clusters. Comparisons of brightness contoured ATS images with radar images from BOMEX test the validity of associating deep convection with very bright clouds. The enhancement technique is then applied in a census of Atlantic cloud clusters, and in case studies of individual clusters.

It is shown that in spite of difficulties involving control of the ATS signal, enhancement is an effective, precise tool for isolating selected features of ATS images. Comparisons of ATS and radar images establish a high correlation of bright areas on ATS with large radar echoes; therefore, enhanced ATS pictures emphasizing the upper levels of the brightness range effectively isolate deep convection. The brightness structure of convective clouds is such that they can be studied over a three-to four-hour period around local noon on pictures uncorrected for changes of incident and reflected radiation. A simple cosine law correction for incident radiation can appreciably extend this period.

The census and case studies show that the eastern Atlantic was at least as convectively active as the western Atlantic during June and July, 1969, and had a significantly greater total area of cloud clusters in 1969 and 1970. Convective cores have a great range of size, spacing, and lifetime: nevertheless, an ordering invariably can be perceived. This most often is in the form of lines or bands; waves, spirals, or solitary cores are also observed. Lifetimes are a few minutes to several hours or more; large cores last longer. Displacement of cloud clusters is accomplished by a complex combination of band and cell movement and propagation. Structure, as evidenced by core behavior, is varied and complex.

Save